Morus (plant)

Lore & Background

Mulberries have been cultivated for centuries, with black mulberry imported to Britain in the 17th century in hopes of supporting silkworm cultivation. The white mulberry (Morus alba) is the species most preferred by silkworms and is ecologically important as their sole food source. The fruit and leaves are used in pies, tarts, wines, cordials, and herbal teas, and in Armenia, mulberries are used to make homemade oghi (moonshine) and syrup known as doshab. Mulberries are fast-growing when young and can grow to 24 meters tall. The leaves are alternately arranged, simple, often lobed and serrated. The trees can be monoecious or dioecious. The fruit is a multiple, about 2–3 cm long, and has a sweet flavor when fully ripe. All parts of the plant except the ripe fruit exude a milky sap that is mildly toxic and can cause skin rash. Unripe green fruit may cause nausea and hallucinations. Male mulberry trees produce pollen that can trigger asthma, while female trees are often considered lower in allergy potential, though not universally allergy-free. In North America, white mulberry is considered an invasive exotic and has taken over extensive tracts from native plant species, including the red mulberry. It is also regarded as invasive in Brazil and some states of Australia. The closely related genus Broussonetia is also commonly known as mulberry, notably the paper mulberry (Broussonetia papyrifera). Despite similar appearance, mulberries are not closely related to raspberries or blackberries, which belong to the Rosaceae family.

Reader's Guide

Morus, the mulberry genus, holds significant ecological and economic importance. Its leaves are the sole food source for the silkworm (Bombyx mori), making it foundational to the silk industry. The three most common species—white, red, and black mulberry—are cultivated worldwide for their fruit, which is used in pies, wines, and traditional medicines. Recent chromosome-level genome assemblies have been published for several species, providing comparative genomic resources. Mulberries are fast-growing trees that can reach 24 meters and are adaptable to a wide variety of conditions. However, white mulberry is considered invasive in parts of North America, Brazil, and Australia, where it displaces native species. The plant also has notable toxicity: all parts except ripe fruit contain a mildly toxic latex, and unripe fruit can cause nausea and hallucinations. Male trees produce abundant pollen that can trigger asthma, while female trees are allergy-free. Mulberries are also used as animal fodder and for making durable baskets. Their nutritional profile includes high vitamin C and iron content. Overall, Morus is a genus of both cultural and agricultural significance, with a complex taxonomy and a dual role as a cultivated resource and an invasive species.

Did You Know?

• The three most common mulberry species are named for the color of their fruit, not the dormant buds.
• White mulberry (Morus alba) is native to northern China, not South Asia, and is the species most preferred by silkworms.
• All parts of the mulberry plant except the ripe fruit exude a milky sap that is mildly toxic and can cause skin rash.
• Female mulberry trees are often considered lower in allergy potential, but they are not universally allergy-free, and an OPALS rating of 1 is not a universally established fact.

Taxonomic Complexity and Genomic Resources

Morus occupies a fascinating and contentious position in botanical classification. While the genus is generally recognized as containing 19 species and roughly 64 subordinate taxa, over 150 species names have been published throughout history, and fewer than 20 are accepted by the vast majority of authorities. The three most commonly referenced species—white (M. alba), red (M. rubra), and black (M. nigra)—are distinguished by the color of their dormant buds rather than their fruit. Widespread hybridization, in which the resulting hybrids remain fertile, further muddies the taxonomic picture. Fossil evidence places Morus in the Pliocene record of the Netherlands, suggesting a long evolutionary history. Importantly, mulberries belong to the Moraceae family alongside figs and jackfruit, and while they share the Rosales order with raspberries and blackberries, they are not closely related to those brambles, which fall under Rosaceae. The closely related genus Broussonetia, home to the paper mulberry, is also colloquially called mulberry. Recent chromosome-level genome assemblies for several species, including M. alba, M. atropurpurea, M. notabilis, and M. macroura, now provide comparative genomic tools to untangle this tangled lineage.

Global Spread and Ecological Footprint

Morus alba is native to South Asia yet has been so widely distributed that it now grows across Europe, Southern Africa, South America, and North America. The black, red, and white mulberries are widespread throughout Southern Europe, the Middle East, Central Asia, Northern Africa, and the Indian subcontinent, where the tree and its fruit carry names in numerous regional dialects. In Greece, the Peloponnese was known in the Middle Ages as Morea, a name derived from the Greek word for mulberry, mouria. Black mulberry reached Britain in the 17th century, imported with the hope of supporting silkworm cultivation, and found a place in folk medicine, particularly for treating tapeworms. In North America, white mulberry is regarded as an invasive exotic that has displaced native species, including the indigenous red mulberry. Australia presents a curious case: two native species, Hedycarya angustifolia and Pipturus argenteus, carry the mulberry name but belong to entirely different families, while the exotic Morus species are commonly grown in backyards. White mulberry is classified as an environmental weed in Queensland and New South Wales.

Cultivation Practices and Cultivar Diversity

Mulberry trees are remarkably fast-growing in their youth and can reach heights of 24 metres. They can be propagated from seed, a method often recommended because seedling-grown trees tend to develop better shape and health, though such trees may require up to ten years before bearing fruit. More commonly, growers use large cuttings that root readily. In organized plantations, saplings eight to ten months old are set out in block formations with spacing of 1.8 by 1.8 metres or 2.4 by 2.4 metres, and are pruned annually during the monsoon season to a crown height of 1.5 to 1.8 metres, retaining a maximum of eight to ten shoots. Grafting is another key technique: scion wood can be attached to dormant trees in winter, and one practical application is converting a pollen-producing male tree into an allergy-free female by grafting female scions onto a trunk that has been cut back. A rich diversity of cultivars has been selected from M. alba, M. nigra, M. rubra, M. macroura, and their hybrids, including names like Chelsea, Illinois Everbearing, Shangri-La, Thai Dwarf, and Silk Hope, each adapted to different climates and growing conditions.

Toxicity, Allergenicity, and Practical Cautions

While ripe mulberry fruit is sweet and enjoyable, the rest of the plant warrants caution. Every part other than the ripe berry can exude a milky latex sap that is mildly toxic if swallowed, producing digestive distress and, in larger quantities, hallucinations. The sap also acts as a skin irritant capable of triggering rashes. Unripe green fruit carries its own risks, including nausea, cramping, and hallucinogenic properties, and even ripe berries have a notable laxative effect that can lead to diarrhea if consumed in excess. Perhaps the most significant modern concern is pollen. Only male mulberry trees produce pollen, but that lightweight pollen can be inhaled deeply into the lungs and trigger asthma in sensitive individuals. As a result, some North American cities have enacted bans on planting mulberries to protect allergy sufferers. A practical horticultural response is grafting: by cutting a problematic male tree back to the trunk and attaching female scions, growers can eliminate the pollen source while retaining the tree's structure, provided all new growth from below the graft is consistently removed.